The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft engine nacelle allows channeling external air toward this engine, and providing high-velocity ejection of this air to provide the necessary thrust.
In the bypass turbojet engines, the airflow blown by the fan is divided, downstream thereof, into a primary flow (also called “hot” flow) which penetrates into the heart of the turbojet engine to undergo therein several compressions and an expansion, and into a secondary flow (also called “cold” flow), which circulates within a substantially annular flow path, defined on the one hand by an engine fairing (internal fixed structure, also called “IFS”) and on the other hand by the outer fairing of the nacelle.
The cold airflow, coming out downstream of the nacelle via an outlet nozzle defined by the downstream edge of this nacelle, provides the essential part of the thrust.
In the case of engines with a very high dilution rate, for aerodynamic optimization reasons to provide a proper operation of the fan and also to optimize fuel consumption, it is quite advantageous to adjust the cold airflow outlet section downstream of the nacelle: it is indeed useful to increase this section during takeoff and landing phases, and reduce it during the cruise phases: this is often referred to as adaptive nozzle, or even “VFN” (Variable Fan Nozzle).
Examples of such adaptive nozzles are known for example from patent applications FR10/52971, FR10/53282, FR10/57240 filed by the applicant.
Conventionally, the variation of the cold flow outlet section is carried out by means of hydraulic or electromechanical actuators, allowing displacing all or part of the outer fairing of the nacelle.
The use of such actuators results in additional weight, space and cost. Their integration into the nacelle, already overcrowded with a large number of members, presents a number of technical difficulties.